1. Field of the Invention
The present invention is directed to the structure of an electronic device, such as personal computers and word processors, and more specifically, to a liquid crystal display (LCD) device equipped with the electronic device and a method of manufacturing a reflection layer in the liquid crystal display device. The present invention may also be applied to an electro-optical device having the liquid crystal display device.
A xe2x80x9csemiconductor devicexe2x80x9d as used herein refers to a general device activated by a semiconductor. Therefore, the above-noted liquid crystal display device and the electro-optical device also fall within a category of semiconductor device. For clarification, the terms of xe2x80x9cliquid crystal display devicexe2x80x9d and xe2x80x9celectro-optical devicexe2x80x9d are separately used herein.
2. Description of Related Arts
A reflection type liquid crystal display device is known. The reflection type liquid crystal display device is more advantageous than a transmission type liquid crystal display device in that a lower power consumption may be achieved with the reflection type since no back light is used. The reflection type liquid crystal display device has also been increasingly required for a direct-vision type display for mobile computers and video cameras.
FIG. 11 is a schematic view showing an example of a conventional structure. Referring to FIG. 11, between a substrate 10 and an opposing substrate 17 are provided switching elements 11 such as thin film transistors, an interlayer insulating film 12, pixel electrodes 13, an orientated layer 14, a liquid crystal layer 15, another orientated layer 14, and an opposite electrode 16 in the stated order from the top surface of the substrate 10. Incident light 20 is reflected by the pixel electrodes 13 to generate a reflection light 21. It is to be noted that although all components are not shown in FIG. 11, which is a schematic view, a number of switching elements and a number of pixel electrodes are formed in a matrix on the surface of the substrate 10.
The reflection type liquid crystal display device utilizes an optical modulating action of the liquid crystal to select the state where the incident light is reflected by the pixel electrodes to be outputted to the outside of the device and the state where the incident light is not outputted to the outside of the device, thereby allowing for the light or dark indication, and a combination thereof would allow an image to be displayed. Each pixel electrode is made of a metal with a high refractive index such as aluminum, and is electrically connected to a switching element such as a thin film transistor.
Such an operational principle causes a phenomenon in which in a displaying state such as a light display, that is the state where the incident light from the external is reflected by the pixel electrodes to be outputted to the external of the device, the display attained by reflecting the incident light by the pixel electrodes as it is, like a mirror, may glare or darken depending upon the viewing angle. In other words, there occurs a phenomenon where the angle of vision may be narrowed.
This is caused by the fact that the reflection state of the incident light differs depending on the viewing angle of the user. In order to avoid such a problem, a need arises to devise the incident light so as to be reflected diffusely on the pixel electrode.
In general, to obtain a diffused reflection, the surface of the pixel electrode made of a metal material is subjected to light etching to form a fine concave or convex portion thereon.
Hitherto, a problem has arisen in which the reflectivity of the refection layer is lowered due to the formation of an orientated layer with a high refractive index on the reflection layer (pixel electrodes made of a metal material). For example, in the case where an orientated layer (having the reflectivity of 1.6) is formed on a vapor-deposited aluminum layer (having the reflectivity of 91.6%), the reflectivity is lowered to 87.4% in calculation, or is lowered to approximately 85% to 86% according to an actual experiment.
In addition, conventionally, formation of a concave or convex portion on the reflection layer causes a reflectivity to be reduced in nature.
The conventional method of forming the reflection layer on which the concave or convex portion is formed by etching also encountered a limitation in terms of the depth of the concave or convex portion to be made deep. Accordingly, there was a problem with the conventional reflection layer (pixel electrode) in terms of brightness applicable to a liquid crystal display device (particularly, to a direct viewing reflection-type liquid crystal panel), since the reflection and diffused reflection of light (including diffusion and scattering) were not sufficient.
The present invention has been made to solve the foregoing problems, and therefore has as an object of the present invention to provide a structure of a liquid crystal display device comprising a reflection layer in which an incident light is reflected and reflected diffusely more efficiently compared to the prior art, and a method of manufacturing the same.
According to a first aspect of the present invention disclosed in this specification, there is provided a liquid crystal display device comprising:
a pixel electrode made of a metal material, which is formed over a substrate; and
a reflection layer formed of a dielectric multi-layer film, which is formed on the pixel electrode, characterized in that a concave or convex portion is formed on the surface of the pixel electrode.
In furtherance of the foregoing structure, the dielectric multi-layer film comprises a structure in which a thin film with a low reflective index and a thin film with a higher reflective index are laminated,
film thickness d1 of the thin film with a lower reflective index is so adjusted as to satisfy 400 nmxe2x89xa6xcex1xe2x89xa6500 nm (xcex1=4n1d1), where the film thickness and the reflective index of the thin film with a low reflective index are d1 and n1, respectively, and
a film thickness d2 of the thin film with a high reflective index is so adjusted as to satisfy 450 nmxe2x89xa6xcex1xe2x89xa6700 nm (xcex2=4n2d2), where the film thickness and the reflective index of the thin film with a high reflective index are d2 and n2, respectively.
In furtherance of the foregoing structure, the pixel electrode is made of aluminum, a material containing aluminum as a main component, silver, or a material containing silver as a main component.
In furtherance of the foregoing structure, the pixel electrode is formed on an interlayer insulating film in contact therewith, the interlayer insulating film being provided with a concave or convex portion formed on its surface.
In furtherance of any one of the foregoing structures, a liquid crystal is sealed between a pair of substrates, the liquid crystal display device comprising the pixel electrode arranged in a matrix manner on one substrate, a thin film transistor connected to the pixel electrode, and a reflection layer.
According to another aspect of the present invention disclosed in the present specification, there is provided a method of manufacturing a liquid crystal display device, characterized by comprising the steps of:
forming a switching element on a substrate;
forming a pixel electrode connected to the switching element, the pixel electrode being provided with a concave or convex portion on its surface; and
forming a dielectric multi-layer film formed of a dielectric film on the top surface of the pixel electrode.
In furtherance of the foregoing structure, the step of forming the pixel electrode having the concave or convex portion on its surface comprises a step of forming a pixel electrode on an interlayer insulating film having the concave or convex portion on its surface.
Further, in the foregoing structure, the step of forming the pixel electrode having the concave or convex portion on its surface comprises a step of etching the surface of the pixel electrode.
Still further, in the foregoing structure, the step of forming the pixel electrode having the concave or convex portion on its surface comprises a step of subjecting the pixel electrode to an anodic oxidation.
Yet further, in the foregoing structure, the step of forming the pixel electrode having the concave or convex portion on its surface comprises a step of forming protrusions by heating.
Further, in any one of the foregoing structures, the step of forming the dielectric multi-layer film comprises a step of coating by spin coat.
Furthermore, in any one of the foregoing structures, the step of forming the dielectric multi-layer film comprises a step of a sputtering method or a vacuum evaporation method.